If there is a VM bug, or you select inappropriate flags for a test run, such that the VM fails to run, you get an error in the log as follows:

 Error: failed to get JDK properties for c:\ade\mesos\work_dir\jib-master\install\2020-05-12-0722149.david.holmes.jdk-dev3\windows-x64-debug.jdk\jdk-15\fastdebug\bin\java -XX:MaxRAMPercentage=3 -XX:+UseZGC -Djava.library.path=c:\ade\mesos\work_dir\jib-master\install\2020-05-12-0722149.david.holmes.jdk-dev3\windows-x64-debug.test\hotspot\jtreg\native; exit code 1

but the actual output of the command is not captured, so if you need to find out the actual error you have to try and recreate the command - which can be a problem if it happened in the test system and you don't have direct access to the platform where it failed.

It's possible this is captured in some other file, but it would be most useful to see it directly in the main log.